Significance of metabolism in medicine

● hereditary enzyme defects

● diabetes, atherosclerosis, gout

● antimetabolites in the chemotherapy of cancers and infections

● inactivation and elimination of xenobiotics and drugs

Catabolic and anabolic reactions

© Michael Palmer 2014

Diversity of metabolism: pathways in plants and bacteria

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Types of foodstuffs

● carbohydrates

● protein

● fat

● nucleic acids

Breakdown of foodstuffs: Overview

© Michael Palmer 2014

The digestive system

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Intestinal organs: functional overview

© Michael Palmer 2014

The portal circulation

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Liver tissue structure

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Blood flow and bile flow within the liver lobule

© Michael Palmer 2014

The stomach: functions of gastric acid

● HCl, pH 1–2

● secreted by specialized cells in the mucous membrane (parietal cells)

● kills germs contained in food; patients with lack of gastric acid are at increased risk of intestinal infection

● denatures food proteins and makes them accessible to cleavage by proteases

Gastric acid and pepsin in protein digestion

© Michael Palmer 2014

Function of the exocrine pancreas

● secretion of digestive enzymes

○ amylase

○ proteases, peptidases

○ lipases

○ DNAse, RNAse

● secretion of bicarbonate to neutralize gastric acid

Roles of bile in digestion

● Bile acids solubilize triacylglycerol and make it accessible to pancreatic lipase

● Bicarbonate contributes to the neutralization of gastric acid

The small intestine

© Michael Palmer 2014

Microscopic structure of the small intestine

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Amylose and amylopectin are polymers of α-D-glucose

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Amylase breaks down starch to maltose and isomaltose

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Mechanism of glucose uptake from the gut

© Michael Palmer 2014

The large intestine

● Anaerobic milieu—99% of all bacteria in the large intestine are strict anaerobes

● Bacteria degrade non-utilized foodstuffs, reducing osmotic activity of gut content

● Mucous membrane recovers water and electrolytes

● Bacterial metabolism releases potentially toxic products (e.g.  ammonia), which are taken up and inactivated by the liver

© Michael Palmer 2014

A more realistic metabolic map

© Michael Palmer 2014